Machine gun testing device



May 29;, 1951 G. E. MOPHERREN 2,554,714

MACHINE GUN TESTING DEVICE Filed Aug. 20, 1945 4 Sheets-Sheet 1 May 29,1951 G. E. MCPHERREN MACHINE GUN TESTING DEVICE Filed Aug. 20, 1945 4Sheets-Sheet 2 NMMW,

mii

kw, uh

iii-ii!!! May 29, 1951 G. E. M PHERREN MACHINE GUN TESTING DEVICE 4Sheets-Sheet 4 Filed Aug. 20, 1945 MNN Patented May 29, 1951 UNITEDSTATES MACHINE GUN TESTING DEVICE,

Glen E. McPherren, San Diego, Calif., assignor to Consolidated VulteeAircraft Corporation, San Diego, Calif., a corporation of DelawareApplication August 20, 1945, Serial No. 611,419:

Claims. 1

The present invention relates to devices for use in testing machine gunsas well as the feed of ammunition thereto.

With the advent of a remote firing machine gun which is mounted in aturret or other structure on an airplane and has the cartridge belt fedto it by way of a flexible chute, there has arisen the need or necessityto experiment with the passage of the belt to the gun. Only in this wayis it possible to determine how smoothly or satisfactorily the cartridgebelt is fed through the feed chute to the gun and where and Whystoppages occur. In the modern airplane machine gun turret with its wideangles of fire much effort has been placed on perfecting smooth feedingfeed chutes to insure a constant supply of ammunition to the gun with aminimum amount of pull on the cartridge belt regardless of the angle atwhich the gun may be fired. In addition to the foregoing it has beennecessary to conduct tests or experiments regarding the disposal of theammunition links and the empty cartridges after the belt passes throughthe gun. As the cartridges are fired, the ammunition belt, by the actionof the ejector mechanism of the gun, is no longer a continuous belt butis broken up into separate links and empty cartridges. The separatelinks and empty cartridges are ejected rapidly and violently from thegun and either fall into a specially designed container or onto thefloor of the turret in which the machine gun is mounted. Unlessexperiments are made to ascertain what happens to the links and emptycartridges as they are ejected from the gun the possibility exists thatthe ejected links and cartridges may disable or foul the operatingmechanism of the turret or the gun mount at a crucial moment.Heretofore, the aforementioned tests and experiments have made itnecessary either to mount the turret with the machine gun therein on aspecially built frame and transport it to a suitable firing range or tofly the airplane with the turret to some safe area and there test forall conceivable stoppages and malfunctions. In addition such tests andexperiments have required the use of live ammunition and hence have beenextremely costly.

The primary object of the invention is to provide a device which willfeed dummy ammunition through a machine gun at the guns normal rate offire to the end that the feed of the cartridge belt to the gun may betested without firing live ammunition and it is not necessary either tomount the gun turret on a specially built frame or transport theairplane on which the machine gun fi l turret is mounted to a suitablefiring range. By providing such a device the feeding of the ammunitionor cartridge belt to the gun, the working of the operating parts of thegun, and the ejection of the separate links and cartridges may beobserved without the necessity of utilizing or firing live ammunition.

Another object of the invention is to provide a device of thelastmentioned character which is pneumatically operated and servesrapidly and repeatedly to reciprocate or shuttle the bolt of the machinegun to which it is applied.

Another object of the invention is to provide a machine gun testingdevice of the type and character under consideration, which comprises acylinder-piston unit the piston of which. is operatively connected tothe bolt of the gun.

A further object of the invention. is to provide a testing device of thelastmentioned character in which the cylinder-piston unit is designed tobe substituted for the oil buffer body in the receiver of the machinegun and has means whereby it may be attached to the barrel extension ofthe gun.

A still further object of the invention is to provide a machine guntesting device which is generally of new and improved construction andis characterized by extremely high efficiency of operation andsimplicity of design.

Other objects of the invention the various advantages andcharacteristics of the present machine gun testing device will beapparent from a consideration of the following detailed description.

The invention consists in the several novel features which arehereinafter set forth and are more particularly defined by the claims atthe conclusion hereof.

In the drawings which accompany and form a part of this specification ordisclosure and in which like numerals of reference denote correspondingparts throughout the several views:

Figure l is a side elevation of a machine gun having applied thereto atesting device embodying one form of the invention, certain parts of thereceiver of the gun being broken away or omitted for purposes ofillustration;

Figure 2 is an enlarged side view of the testing device of Figure 1,illustrating in detail the manner in which the cylinder-piston unit isattached or connected to the barrel extension of the gun and also themanner in which the piston of the unit is operatively connected to themachine gun bolt;

Figures 3, 4 and 5 are vertical longitudinal sections of thecylinder-piston unit, illustrating in detail the construction design andmode of operation of the various component parts of the unit and showingthe manner in which the piston operates in response to reciprocationthereof to actuate or shuttle the bolt of the machine gun;

Figure 6 is a horizontal section on the line -6 of Figure 3;

Figures '7, 8 and 9 are vertical transverse sections taken respectively,on the lines 'l--'l, 8--8 and 9-& of Figure 3; and

Figure 10 is a fragmentary vertical longitudinal section of a machinegun having applied thereto a testing device embodying a second ormodified form of the invention.

The testing device which is shown in Figures 1 to 9, inclusive, of thedrawings constitutes one form or embodiment of the invention. It isadapted for use in connection with a machine gun ii] and serves ashereinafter described in detail to feed a cartridge belt with dummycartridges through the gun in order that the feeding of the belt to thegun, the working of the operating parts of the gun, and the ejection ofthe separate links and cartridges from the gun may be observed withoutthe necessity of utilizing or firing live armunition. The machine gun isis the well known Browning gun which is designed to be mounted in aturret or on any other suitable supporting structure on an airplane andto have the ammunition or cartridge belt fed to it by a flexible chute.In general, the gun comprises a receiver H, a barrel I2, a barrelextension l3, and a bolt M. The receiver l i is horizontally elongatedand forms a housing for the barrel extension E3, the bolt 54, andcertain other operating parts of the gun. It consists of a pair oflaterally spaced side walls i5, a top wall It, a bottom wall ll, and afront wall I3 and has at the rear end thereof a back plate 19. The sidewalls l5 of the machine gun receiver are spaced apart by the top, bottomand front walls. The front portion of the bottom wall is disposed at ahigher elevation than the rear portion and is joined to the latter by avertically extending cross wall 29. The front wall l8 of the receiver isprovided with a collar 2! to which is connected one end of a barreljacket 22. The back plate I9 is slidably connected to the rear ends ofthe side walls 55 and has any suitable latch means for releasablysecuring it in its operative position. The barrel l2 has the front endthereof disposed in the barrel jacket 22 and its rear end positionedwithin the front portion of the receiver H. The barrel extension i3 ismounted for longitudinal sliding movement in the central portion of thereceiver and embodies a pair of laterally spaced sides 24 and a crosswall 25. Said cross wall is connected to, and extends between, the frontends of the sides of the barrel extension and has a socket 26. The rearend of the barrel l2 fits within the socket and is re movably secured inplace by means of a screw thread connection 2'1. The rear ends of thesides 24 of the barrel extension are provided with depending extensions28 which, as well understood in the art, are adapted in connection withthe forward sliding movement of the barrel extension to strike againstthe vertically extending cross wall 28 and thus limit or restrict theforward sliding movement of the barrel extension and the barrel withrespect to the receiver H of the machine gun Ill. The bolt I l overliesthe barrel extension l3 and is slidably W l lllmmn connected to thelatter by way of horizontally extending side ribs which fit withingrooves 30 in the inner portions of the sides 24 of the barrelextension. The ammunition or cartridge belt for the machine gun is fedinto the receiver through an elongated opening in one of the receiverside walls l5. In connection with normal operation of the machine gunll) the barrel extension and bolt are forwardly disposed when acartridge is fired in the barrel i2. As soon as the cartridge ..s firedthe force of recoil carries the barrel, the barrel extension and thebolt backwards short distance. This motion serves to unlock the boltfrom the barrel extension and the bolt throws back farther toward theback plate [9 against a spring 3!. Rearward movement of the barrelextension and the barrel is checked by way of an oil buffer body (notshown) which is disposed in the rear lower portion of the receiver andextends between the lower end of the back plate 59 and the rear end ofthe barrel extension l3. During the long rearward motion of the bolt theempty cartridge is withdrawn from the rear end of the barrel. When thebolt is slid or shifted forwards by the spring 3| the empty cartridgecase is ejected from the receiver and the next following cartridge isinserted into the rear end of the barrel as well understood in the art.

The testing device which is shown in Figures 1 to 9, inclusive, isdesigned to be substituted for the oil buffer body which as previouslypointed out, is normally disposed in the rear lower portion of themachine gun receiver II. It is operated pneumatically and serves whenoperated while in its operative position to rapidly and repeatedlyreciprocate or shuttle the machine gun bolt it. As its principal partsor components the testing device comprises a horizontally elongatedcylinder block 32, a cylinder 33, a piston 3 and a piston rod 35.

The cylinder .lock 32 is formed of any suitable metal and, as shown inthe drawings, is rectilinear in cross section. It is shaped and designedto fit within the rear lower portion of the machine gun receiver l l andalso to have the front end thereof abut against the rear end of thebarrel extension l3 and its rear end abut against the lower end of theback plate IS. The length of the cylinder block is such that when thetesting device is in its operative position the block together with thecross wall 20 locks the barrel extension l3 and the barrel I2 againstsliding movement relatively to the machine gun receiver ii. The width ofthe cylinder block corresponds to the width of the receiver interiorwith the result that the side walls i5 of the receiver hold the cylinderblock against sidewise displacement relatively to the receiver. Theupper portion of the cylinder block is provided with a cylindricallongitudinally extending open ended bore in which the cylinder 33 ismounted for limited longitudinal sliding movement. The front end of thecylinder block 32 of the testing device is releasably connected to therear end of the aforementioned barrel extension I3 by a pair of side byside horizontally extending locking keys 37. The rear ends of these keysare provided with enlarged heads 33 and fit in grooves 39 in the frontportions of the side bases of the cylinder block. As shown in thedrawings the grooves are shaped conformably to the rear ends of thelocking keys 31. The front ends of such keys embody depending lugs 40and fit within correspondingly shaped grooves 4| in the outer faces ofthe depending extensions at the rear ends of the sides 24 of the barrelextension l3. In

mounting the testing device with respect to the machine gun ID the backplate [3 is first removed from the receiver II by releasing theaforementioned latch means and then sliding it out of connected relationwith the rear end of the receiver. moved from the receiver and thebarrel extension l3 is'slid rearwards until the rear end thereof isdisposed exteriorly of the receiver. After so shifting the barrelextension the front en d of the cylinder block 32 is placed in abutmentwith the rear end of the barrel extension and the two locking keys 3'!are manipulated in their operative position wherein the rear endsthereof are disposed in the grooves 39 and their front ends are disposedin the grooves 4|. After so positioning the two locking keys thecylinder block 32 is shifted forwards until it is disposed within therear lower portion of the receiver interior. After this step oroperation the back plate 19 of the machine gun is returned to, andlatched in, its normal position wherein it closes the rear end of thereceiver interior.

The bottom portion of the cylinder block 32 is provided with an L-shapedinlet duct 42 for air under pressure and is also provided with a pair of,L-shaped discharge ducts 43 and 44. The inlet duct 42 is formed in therear lower portion of the cylinder block and consists of alongitudinally extending branch 42a and a transversely extending branch42b at the inner end of the branch 42a. The outer end of the branch 42ahas associated with it a fitting 45 whereby a hose or flexible pipeleading from a suitable source of air under pressure may be connected tothe inlet duct 42. The receiving end of the fitting 45 extends through acutout 46 in the back plate l9 of the machine gun and the discharge endof the fitting 'is connected by a screw thread connection 41 to theouter end of a longitudinally extending branch 42a of the inlet duct 42.The transversely extending branch 426 of the inlet duct is located inthe central portion of the cylinder block and has the upper portionthereof in intersecting and communicating relation with the centrallower portion of the cylindrical open ended bore 36. The discharge duct43 is formed in the front end of the cylinder block. It consists of atransversely extending branch 43a and a longitudinally extending branch43b. The branch 43a of the duct 43 is disposed directly forward of, andin parallel relation with, the transversely extending branch 42b of theinlet duct 42 and has the upper portion thereof in intersecting andcommunicating relation with the central lower portion of the bore 36.The longitudinally extending branch 43?) of the discharge duct 43 leadsforward from the outer end of-the transversely extending branch 43a andhas the front end thereof in communication with one end of a groove 48which extends part way around the front portion of the cylindricallongitudinally open ended bore 36 in the upper portion of the cylinderblock 32. As shown in the drawings the groove 48 is disposed inward ofthe front face or extremity of the cylinder block. The other dischargeduct, that is, the duct 44, is formed in the rear lower portion of thecylinder block and comprises a transversely extending branch 44a and alongitudinally extending branch 44b.

The branch 44a is disposed directly rearwards of and in parallelrelation with, the transversely "extending branch 42b of the inlet duct42 and has Thereafter the oil buffer body is reits upper portion inintersecting and communicating relation with the lower central portionof the bore 36. The longitudinally extending branch 44b of the dischargeduct 44 leads rearwards from the outer end of the branch 44a and has itsrear end in communication with one end of a groove 49 around the rearportion of the bore 36. The groove 49 extends part way around the boreand is disposed inward of the rear face or extremity of the cylinderblock. i

The cylinder 33 which as previously pointed out is mounted forlongitudinal sliding movement in the bore 35 in the cylinder block 32 istubular in design and has a cylinder head 50 at the front end thereofand a cylinder head 5| at its rear end. The head 56 is provided with acentrally positioned bore 52 and is secured in place by way of a screwthread connection 53. A spiral compression spring 54 is suitably mountedon the inner end face of the cylinder head 59 and extends concentricallyaround the centrally disposed bore 52. A port 55 is formed in the frontend of the cylinder and this is disposed directly inward of thecylinder. head 50 and is in registry with the groove 48 thatcommunicates with the front end of the longitudinally extending branch43b of the discharge duct 43. The cylinder head 5| is imperforate. Itserves to close or seal the rear end of the interior of the cylinder 33and is secured in place by .a screw thread connection 56. A spiral orhelical compression spring 51 is mounted on the central portion of theinner face of the cylinder head 5|. The rear end of the cylinder 33 isprovided with a port 58 and this is disposed directly in front of thecylinder head 5| and registers with the groove 49 which as heretoforedescribed communicates with the rear or outer end of the longitudinallyextending branch 44b of the discharge duct 44. Longitudinal slidingmovement of the cylinder 33 with respect to the cylinder block 32 islimited by way of a connection in the form of a groove 59 and a pin 60.The groove 53 is formed in, and extends longitudinally of, the bottomportionof the cylinder 33. The pin 63 extends upward through the bottomportion of the cylinder block and has its upper end disposed in thegroove 53. The cylinder is of such length that when it is slid orshifted forward to its fullest extent as shown in Figure 4 the front endof the cylinder is disposed outward of and seals from atmosphere thegroove 48, the port 55 is disposed opposite to the outer or frontportion of the groove 48, the rear end of the cylinder is disposedadjacent the central portion of the groove 43, and the port 58 ispositioned opposite the front or inner portion of the groove 49. Vthenthe cylinder is shifted rearwards to its fullest extent as shown inFigure 5 the rear end of the cylinder is disposed outwards of and sealsfrom atmosphere the groove 49, the front end of the cylinder is disposedadjacent the central portion of the groove 48, and the port 55 ispositioned opposite the inner portion of the groove 48. The centrallower portion of the cylinder 33 is provided with a cutout Bl which whenthe cylinder is shifted forwards to its fullest extent, bridges andestablishes communication between the transversely extending branches42b and 43a of the ducts 4E and 43 and when the cylinder is shifted orslid rearthe front end of the cylinder 33 by way of the inlet duct 42,the cutout 65, the discharge duct 43,'the groove 48, and the port 55,and the rear end of the cylinder is vented by way of the port 58 and thegroove 49. When the cylinder is shifted or slid rearwards the rear endof the cylinder is supplied with air under pressure by way of the inletduct 42, the cutout the discharge duct 44, the groove do and the port53, and the front end of the cylinder is vented by way of the ports 55and the groove 43.

The piston 34 is mounted in the cylinder 33! to slide or reciprocateback and forth between the cylinder heads 5i and 51. The piston rod 35extends slidably through the centrally disposed bore 52 in the cylinderhead 56 and has the rear end thereof fixedly connected to thecentral'portion of the piston 34. The front end of the piston rod isdisposed between the sides .24 of the machine gun barrel extension isand has its forward extremity operatively connected to the front end ofthe bolt l4 by way of an upstanding arm 62. As shown in the drawings,the lower end of the arm 62 is fixedly connected to the adjacent end ofthe piston rod and the upper end of the arm is shaped to fit snuglywithin a socket 63 in the front end of the bolt 14. As a result of theconnection between the front end of the piston rod and the front end ofthe bolt, the bolt is caused to move back and forth for cartridge beltfeeding purposes in response to reciprocation of the piston 34 in thecylinder 33. When the cylinder and piston are positioned as shown inFigure 4, air under pressure enters the front end of the cylinder ashereinbefore pointed out and causes the piston 34 together with thepiston rod 35 and the machine gun belt I 4 to slide rearwards. Duringrearward sliding movement of the piston the air in the rear end of thecylinder is exhausted to atv mosphere via the ports 58 and the groove49. As soon as the piston reaches the end of its rearward stroke itstrikes against the compression spring 51 with such force that thecylinder 33 is caused to slide rearwards relatively to the cylinderblock 32. Rearward sliding of the cylinder is directly attributable tothe fact that the piston slides rearwards at an extremely rapid rate andstrikes the spring ill with considerable force due to the momentum ofthe piston, the piston rod, and the machine gun bolt. .As soon as thecylinder is shifted rearwards so as to cause the cutout iii to bridgeand establish communication between the branches 42b and 44a of theducts 42 and 44 air under pressure enters the rearj end of the cylinderand causes the piston together with the piston rod and the machine gunbolt to slide forwards. During forward sliding movement of the pistonthe front end of the cylinder is vented via the port 55 and the groove43. As soon as the piston reaches the end of its forward stroke itstrikes against the compression spring 5 1 and shifts the cylinderforwards into a position wherein the aforementioned cycle again takesplace. The speed or rapidity of reciprocation of the piston its isdependent upon the pressure of the air which enters the cylinder throughthe ports 55 and 58. It is contemplated that in normal use of thetesting device the pressure of the air wil be such that the piston willreciprocate at a speed correspending to the machine guns normal rate offire. The compression springs 5d and 5? serve to separate the pistonfrom the cylinder heads when the piston reaches the ends of its strokesand thus assure admission of air under pressure into the cylinder.

In using the testing device of Figures 1 to 9, inclusive, the device ismanipulated into its operative position wherein as previously pointedout it serves as a substitute for the oil buffer body in the rear lowerportion of the interior of the machine gun receiver II. In connectionwith manipulation of the device into place the upper end of the arm 62is inserted into the socket 63 in the front end of the bolt l4 beforethe barrel extension 53 and the cylinder block 32 are slid into thereceiver. When it is desired to utilize the testing device it is onlynecessary to supply air under pressure to the fitting 45. As soon as theflow of air under pressure to the fitting commences, the piston 34 israpidly reciprocated and operates through the medium of the piston rod35 to cause the machine gun bolt Hi to slide or shuttle back or forth.Such movement on the part of the bolt results in the cartridge beltbeing fed through the gun. By employing the testing device dummyammunition may be fed through the machine gun to the end that the feedof the belt through the flexible chute leading to the receiver of thegun, the working of the operating parts of the gun, and the ejection ofthe separate links and cartridges from the receiver may be observedwithout the necessity of utilizing or firing live amxnunition.

The testing device of Figures 1 to 9, inclusive, effectively andefiiciently fulfills its intended purpose and is characterized by thefact that it may be manufactured and operated. at a low cost and inaddition may be mounted and removed with facility. It is essentially asubstitute uni for the regular oil buffer body of the machine gun andmakes it possible to test the machine gun and the feed of ammunitionthereto without the necessity of either mounting the turret for the gunon a specially built frame and transporting it to a suitable firing rane or fiying or transporting the airplane with the turret to a safefiring area. In addition to serving as a medium or instrumentality fortesting a machine gun and the feed of ammunition thereto, the device maybe utilized to give a permanent set to the mount for the machine gun. Insuch case no ammunition belt is fed to the machine gun receiver and thedevice as the result of the rapid reciprocation of the bolt produces ahammering action which simulates the normal hammering action resultingfrom firing of the gun and imparts the desired permanent set to themachine gun mount.

The testing device which is shown in Figure 19 constitutes a second ormodified embodiment of the invention. It functions similarly to, andserves the same purpose as, the machine gun testing device of Figures 1to 9, inclusive, but diil'ers therefrom in that it is in the form of aunitary structure which is adapted to be substituted for the barrel, thebarrel extension and the bolt of the machine gun to which it is applied.As its component parts the subject testin device comprises a unit 64, abarrel extension 85, and a bolt 66. The unit 64 includes a cylinderblock 53, cylinder 615, a piston 65), and a piston rod l5) and is thesame as the testing device of Figures 1 to inclusive, except that thefront end of the cylinder block 67, instead of being detachablyconnected to the rear end of the barrel extension, is formed integrallywith the barrel extension. The bolt 66 is slidably con- I collarrearwards.

the end of its rearward stroke.

portion of the back plate.

nected to the barrel extension 65 and has its front end operativelyconnected to the front end of the piston rod 18 by an upstanding arm Hthe lower end of which is fixedly connected to the piston rod and theupper end of which fits within a socket in the front end of the bolt 65.The testing device of Figure 10 includes no conventional barrel on thefront end of the barrel extension 65. It does, however, include a sleeve12 in lieu of a barrel. This sleeve is located directly in front of theextension barrel 65 and has a centrally apertured screw plug 13 in itsfront end. The aperture in the plug is adapted to receive the cartridgesin connection with a machine gun testing operation. The rear end of thesleeve 12 fits within the centrally disposed socket in the verticallyextending cross Wall of the barrel extension, is connected thereto by ascrew thread connection 14, and has an integral inwardly extendingflange i5. An abutment collar 16 is arranged in associated relation withthe rear end of the sleeve '82. This collar is positioned concentricallywith respect to the sleeve and has at its front end an angular outwardlyextending flange H which fits slidably within the rear end of the sleeveand coacts with the inwardly extending flange T to limit rearwardsliding movement of the collar with respect to the sleeve. A rectilinearseries of pairs of opposed conical or dome shaped spring washers-18extends between the plug 13 and the outwardly extending flange '11 onthe front end of the abutment collar 76 and serves to urge the Thelength of the collar '55 is such that in connection with forward slidingof the bolt 66 by the piston 69 the collar is engaged by the front endof the bolt and urged forwards against the force of the spring washers18. Upon release or expansion of the washers the collar moves rearwardssubstantially instantaneously and imparts rearward sliding movement -tothe bolt 66. Such rearward sliding movement on the part of the boltmoves the piston 69 of the unit 64 away from the cylinder head at thefront end of the cylinder 68. The spring action which is occasioned orproduced by the spring washers 18 tends to cause the unit 64 to operateat an extremely high rate of speed and eliminates the necessity ofproviding a spiral or helical compression spring on the inner face ofthe cylinder head at the front end of the cylinder 68.

It is contemplated that when the testing device of Figure is used formachine gun testing purposes a special back plate l9 will be utilizedinstead of the regular or conventional back plate on the rear end of themachine gun receiver. The back plate 19' is like the standard orconventional back' plate except that it includes a spring assembly 86which imparts a quick acting forward force to the bolt 65 when thelatter reaches This spring assembly 80 functions in the same manner asthe spring assembly consisting of the sleeve 12, the plug 13, theabutment collar and the spring Washers I8 and comprises as its parts asleeve BI, a plug 82, an abutment collar 83, and a rectilinear series ofpairs of opposed conical or dished spring washers 8d. The sleeve 8! isin registry with and extends rearwards from an aperture 85in the backplate 19 and has the front end thereof fixedly secured to the aperturedefining The plug 82 fits within the rear end of the sleeve 8! and isadjustably secured thereto by way of a screw thread connection 86. Thefront end of the sleeve 8i is provided with an integral inwardlyextending flange 81. The abutment collar 83 is located adjacent thefront end of the sleeve 8| and embodies an outwardly extending angularflange which fits slidably within the front end of the sleeve and coactswith the flange ti to limit or restrict forward sliding movement of theabutment collar with respect to the sleeve. The washers 86 areinterposed between. the plug 82 and the rear end of the abutment collar83. Said collar is of such length and so positioned that it is engagedand shifted rearwards by the bolt (56 at the endiof the rearward strokeof the bolt. When the bolt reaches the end of its rearward stroke itshifts the abutment collar 83 rearwards against the force of the springwashers 84. When the washers recover their normal position they shiftthe abutment collar 83 forwards substantially instantaneously and impartforward movement to the bolt 65. The spring assembly Bil constitutes arecoil medium for imparting forward movement to the bolt at the end ofthe latters rearward stroke, increases the speed of action of the unit(it and eliminates the necessity of mounting a compression spring ontheinner face of the cylinder head at the rear end of the cylinder 68.

When it is desired to use the testing device of Figure 10 for machinegun testing purposes the regular back plate of the gun is first removed.Thereafter the oil bufier body, the barrel extension, the barrel, andthe bolt of the gun are removed through the open rear end of the machinegun receiver. Upon removal of these parts of the gun the testing deviceis shifted into the receiver and is then secured in place by sliding thespecial back plate 19 into interfitting relation with the rear end ofthe gun receiver. When it is desired to operate the device air underpressure is supplied to the cylinder block 61 of the unit 54. As soon asair under pressure is supplied to the cylinder block the piston 69 israpidly reciprccated and efiects corresponding reciprocation of the bolt66. The bolt 66 is provided with no firing mechanism with the resultthat when it is reciprocated in connection'with feed of a cartridge beltthrough the receiver of the machine gun there is no firing of thecartridges even though the cartridges forming a part of the belt are inthe form of live ammunition. After the testing device of Figure 10 hasserved its purpose it may be removed merely by removing the back plate79 and sliding the device bodily out of the open rear end of thereceiver of the machine gun.

The testing device of Figure 10 like the device of Figures 1 to 9,inclusive, effectively and efiiciently fulfills its intended purposeandis charac terized by the fact that it is extremely quick acting andwill feed a cartridge belt at high speed through the receiver of the gunwith which the device is used. It is comparatively simple in design andmay be installed and removed with facility.

The invention is not to be understood as restricted to the details setforth since these may be modified within the scope of the appendedclaims without departing from the spirit and scope of the invention.

Having thus described the invention, what I claim as new and desire tosecure by Letters Patent is:

l. A device designed for use in testing a machine gun of the type thatembodies a receiver, a barrel extension and a removable bufier unit inthe receiver, and a cartridge feeding bolt slidably connected to thebarrel extension, and comprising a housing adapted to be mounted in thereceiver in place of the buffer unit and having a cylinder therein, apiston mounted slidably in the cylinder, provided with means foroperatively connecting it to the bolt and adapted when reciprocated toshuttle the bolt, and means for alternately supplying air under pressureto opposite ends of the cylinder in order to effect reciprocation of thepiston.

2. A device designed for use in testing a machine gun of the type thatembodies a receiver, a barrel extension disposed in the receiver and,including a pair of laterally spaced sides, a bufier unit mounted in thereceiver behind the barrel extension, and a cartridge feeding boltconnected to the barrel extension so that it is slidable lengthwise ofthe receiver, said device comprising a housing adapted to fit removablyin the receiver behind the barrel extension after removal of the bufferunit and having a, cylinder therein extending lengthwise of thereceiver, a piston slidably mounted in the cylinder, a piston rodconnected to, and extending forwards from, the piston, having the frontend thereof positioned between the sides of the barrel extension andprovided with means for connection to the bolt, and adapted in responseto reciprocation of the piston to shuttle the bolt for cartridge feedingpurposes, and means for alternately supplying air under pressure toopposite ends of the cylinder in order to effect reciprocation of thepiston.

3. A device designed for use in testing a ma-- chine gun of the typethat embodies a receiver with a removable back plate, a barrel extensionin the central portion of the receiver, a bufier unit in the receiverbetween the barrel extension and the back plate, and a cartridge feedingbolt connected to the barrel extension so that it is slidable lengthwiseof the receiver, said device comprising a housing shaped and adapted tofit removably in the receiver between the barrel extension and the backplate after removal of the buffer unit and having a cylinder extendinglengthwise of the receiver, a piston slidably mounted in the cylinder,provided with means for operatively connecting it to the bolt, andadapted when reciprocated to shuttle the bolt for cartridge feedingpurposes, and means for alternately supplying air under pressure toopposite ends of the cylinder in order to effect reciprocation of thepiston.

4. A device designed for use in testing a machine gun of the type thatembodies a receiver With a removable back plate, a barrel extensionmounted in the central portion of the receiver for limited forward andrearward sliding movement, a buffer unit disposed in the receiverbetween the barrel extension and the back plate, and a bolt positionedabove the barrel extension and connected thereto so that it is slidablelengthwise of the receiver, said device comprising a housing shaped andadapted to fit removably in the receiver between the barrel extensionand the back plate after removal of the buffer unit, adapted when inplace to lock the barrel extension against sliding movement, and havinga cylinder therein extending lengthwise of the receiver, a pistonslidably mounted in the cylinder, a piston rod having one end thereofconnected to the piston and its other end provided with means forconnection to the bolt, and adapted in response to reciprocation oi thepiston to shuttle the bolt for cartridge feeding purposes, and means foralternately supplying air under pressure to pl2 posite ends of thecylinder in order to effect reciprocation of the piston.

5. A device designed for use in testing amachine gun of the type thatembodies a receiver with a removable back plate, a barrel extensionmounted in the central portion of the receiver for limited forward andrearward sliding movement and including a pair of laterally spacedsides, a buffer unit disposed in the receiver between the barrelextension and the back plate, and a cartridge feeding bolt positionedabove the barrel extension and connected thereto so that it is slidablelengthwise of the receiver, said device comprising a housing shaped tofit removably in the receiver between the barrel extension and the backplate after removal of the buffer unit, adapted when in place to lockthe barrel extension against sliding movement, and having a cylindertherein extending lengthwise of the receiver, a piston slidably mountedin the cylinder, a piston rod connected to, and extending forwards from,the piston, having the front end thereof positioned between the sides ofthe barrel extension and provided with means for connec tion. to thebolt, and adapted in response to reciprocation oi the piston to shuttlethe bolt, and means for alternately supplying air under pressure toopposite ends of the cylinder in order to effect reciprocation of thepiston.

6. A device designed for use in testing a machine gun of the type thatembodies a receiver, a barrel extension disposed in the receiver andprovided with a slidable breech lock, a buffer unit mounted in thereceiver behind the barrel extension, and a cartridge feeding boltconnected to the barrel extension so that it is slidable lengthwise ofthe receiver and adapted when slid forwards to be locked by the breechlock, said device comprising a housing adapted to be mounted in thereceiver in place of the bufier unit, provided with means for connectingit to the barrel extension and having a cylinder therein, a. pistonslidably mounted in the cylinder, provided with means for operativelyconnecting it to the bolt and adapted when reciprocated to shuttle thebolt, and means for alternately supplying air under pressure to oppositeends of the cylinder in order to eiiect reciprocation of the piston.

'7. A device designed for use in testing a machine gun of the type thatembodies the receiver, a barrel extension disposed in the centralportion of the receiver, provided with a slidable breech look, andincluding a pair of laterally spaced sides, a buffer unit removablymounted in the receiver behind the barrel extension, and a cartridgefeeding bolt connected to the barrel extension so that it is slidablelengthwise of the receiver and adapted when slid forwards to be lockedby the breech lock, said device comprising a housing adapted to bemounted in the receiver behind the barrel extension after removal of thebuffer unit, provided at the front end thereof with means for connectingit to the barrel extension, and having a cylinder therein extendinglengthwise of the receiver, a piston slidably mounted in the cylinder, apiston rod connected to, and extending forwards from, the piston, havingthe front end thereof adapted for disposition between the sides of thebarrel extension and provided with means for connection to the bolt, andadapted in response to reciprocation of the piston to shuttle the boltfor cartridge feeding purposes, and means for alternately supplying airunder pressure to opposite ends of the cylinder in order to effectreciprocation of the piston.

8. A device designed for use in testing a ma- 13 chine gun of the typethat embodies a receiver with a removable back plate, a barrel extensionmounted in the central portion of the receiver for limited forward andrearward sliding movement, provided at its rear end with a slidablebreech lock, and including a pair of laterally spaced sides, a bufierunit disposed in the receiver between the barrel extension and the backplate, and a cartridge feeding bolt connected to the barrel extension sothat it is slidable lengthwise of the receiver and adapted when slidforwards to be locked by the breech lock, said device comprising ahousing adapted to be mounted in the receiver between the barrelextension and the back plate in place of the bufier unit, adapted whenin place to lock the barrel extension against sliding movement, providedwith means at its front end for connecting it to the barrel extension,and having a cylinder therein extending lengthwise of the receiver, apiston slidably mounted in the cylinder, a piston rod connected to, andextending forwards from, the piston, having the front end thereofadapted for disposition between the sides of the barrel extension andprovided with means for connection to the bolt and adapted in responseto reciprocation of the piston to shuttle the bolt, and means foralternately supplying air under pressure to opposite ends of thecylinder in order to effect reciprocation of the piston.

9. A device for use in testing a machine gun of the type that embodies areceiver, a barrel extension and a buffer unit in the receiver, and acartridge feeding bolt mounted to slide relatively to the barrelextension, said device being 14 designed to be mounted in the receiverin place of the buffer unit and embodying a power actuated unit havingmeans for operatively connecting it to the bolt and adapted whenactuated to shuttle the bolt.

10. A device adapted for use in testing a machine gun of th type thatembodies a receiver, a barrel extension and a buffer unit in thereceiver, and a cartridge feeding bolt mounted to slide relatively tothe barrel extension, said device being designed to be mounted in thereceiver in place of the bufier unit and embodying a pneumaticallyactuated cylinder-piston unit having means for operatively connecting itto the bolt and adapted when actuated to shuttle the bolt.

GLEN E. MCPHERREN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Publication, Tine-225 War Dept.,December 15, 1943, Browning Machine Gun Cal. 50 M2, Aircraft Basic. v

